Asymmetric thrust?
Thread Starter
Plastic PPRuNer
Joined: Sep 2000
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From: Rochechouart, France
Asymmetric thrust?
In a big podded twin jet how do you guys (and the airframe) cope with the massive asmmetric thrust produced by losing one at V2?
[...there, I've asked it. Been wanting to for ages but never dared]
[...there, I've asked it. Been wanting to for ages but never dared]
Thread Starter
Plastic PPRuNer
Joined: Sep 2000
Posts: 1,902
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From: Rochechouart, France
Must be a lot of rudder authority! Doesn't it crab horribly?
I visualise it as someone flying along like when kids pretend to be aeroplanes with their arms out and trying to drag them along by one elbow and still keep flying straight. Fascinating business.
Bet you get an aching leg after flying around like that for a while. How much can you trim out?
Thanks for the answers.
I visualise it as someone flying along like when kids pretend to be aeroplanes with their arms out and trying to drag them along by one elbow and still keep flying straight. Fascinating business.
Bet you get an aching leg after flying around like that for a while. How much can you trim out?
Thanks for the answers.
Joined: Mar 2000
Posts: 8,571
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From: Arizona USA
Older 4-engine types....even worse
Yep, 'tis true.
Take the 'ole straight-pipe powered 707-300/400 series with Conway or JT4A engines.
An outboard engine failure with these at V1 (or just after) required a 145 pound push on the rudder.
Not an easy task and still keep the heading within the 5 degree margin.
Gusty winds?
No help from the yaw damper, it had to be switched off for takeoff (and landing).
Take the 'ole straight-pipe powered 707-300/400 series with Conway or JT4A engines.
An outboard engine failure with these at V1 (or just after) required a 145 pound push on the rudder.
Not an easy task and still keep the heading within the 5 degree margin.
Gusty winds?
No help from the yaw damper, it had to be switched off for takeoff (and landing).
Joined: Jun 2004
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From: Australia
As long as you can maintain up to 150 Lb pressure on the rudder Mac, the aircraft is perfectly controllable, and doesn't "crab horribly". That's the certification requirement, or at least it used to be in the era that 411A speaks of. It may have reduced in more recent times, but frankly I don't know if this is so.
150 Lb would exceed the total body mass of some smaller build pilots, I remember smiling whilst watching a small pilot doing assymetric training on a DC4, he had to lift his bum right out of the seat to apply his whole body weight to the rudder.
Regards,
Old Smokey
150 Lb would exceed the total body mass of some smaller build pilots, I remember smiling whilst watching a small pilot doing assymetric training on a DC4, he had to lift his bum right out of the seat to apply his whole body weight to the rudder.
Regards,
Old Smokey
Joined: Jan 2006
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From: on the Blue Planet
Well I guess the inputs in a twin are no bigger than loosing two on the same side on a 4 holer 
(in the ol'days on the 146, we had an instructor who loved chopping 2 engines right or left side (in the sim), after takeoff, speed in the V2 +10 range. As the beast is not climbing with 4, picture the performance with 2 donkeys lost on one side 
).
Our beloved design engineers have always (well almost...) given aircraft big enough rudder to counteract such problems.
Err, 411A, regarding the yaw damper, I doubt it would have been of any help, even had it been switched on. Quite the opposite. Think about the reason it had to be off during T/O & LD...
(in the ol'days on the 146, we had an instructor who loved chopping 2 engines right or left side (in the sim), after takeoff, speed in the V2 +10 range. As the beast is not climbing with 4, picture the performance with 2 donkeys lost on one side ).Our beloved design engineers have always (well almost...) given aircraft big enough rudder to counteract such problems.
Err, 411A, regarding the yaw damper, I doubt it would have been of any help, even had it been switched on. Quite the opposite. Think about the reason it had to be off during T/O & LD...
Joined: Mar 2000
Posts: 8,571
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From: Arizona USA
The older type yaw damper on the 707, F4F, was of the parallel variety, and indeed OFF was the requirement.
This presented the pilot with some handling issues, as the vertical fin on these older models was shorter than later models, so in gusty winds, it was a dutch rollin' bronco....
Later 'fixes' for this was the 39 inch ventral fin fitted, and this helped...some.
The ultimate was on the -320B advanced models, taller vertical fin, no ventral fin, and a much better designed series type full time yaw damper, as on modern types, now.
The older 707's nearly did not make it onto the British register, as David P. Davies insisted they be improved in the handling department...especially the rudder power.
Ha! Even the 'improvements' implemented by Boeing were a tad on the thin side, from my experience in these old aeroplanes...long ago.
This presented the pilot with some handling issues, as the vertical fin on these older models was shorter than later models, so in gusty winds, it was a dutch rollin' bronco....
Later 'fixes' for this was the 39 inch ventral fin fitted, and this helped...some.
The ultimate was on the -320B advanced models, taller vertical fin, no ventral fin, and a much better designed series type full time yaw damper, as on modern types, now.
The older 707's nearly did not make it onto the British register, as David P. Davies insisted they be improved in the handling department...especially the rudder power.
Ha! Even the 'improvements' implemented by Boeing were a tad on the thin side, from my experience in these old aeroplanes...long ago.
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From: Eagan, MN
Was a sim instructor on the C141A in the early 70's. The 2-engine out routine was a physical challenge; after that drill, people would come out of the box with shaking leg, or limping, sometimes unable to walk. When women were first checked out on the equipment, some crewmembers were scandalized that this drill had to be waived for some of the women...glad it was, never resulted in a problem on the line, AFAIK. Sam
